I n t h e c i r c u i t s how n a bov e , t h e b a t t e r y m a i n t a i n s a c on s t a n t p o t e n t i a l b e t w ee n po i n t s 1 a n d 2 ( t h a t i s , t h e i n t e rn a l r e s i s t a n c e o f t h e b a t t e r y i s n e g l i g i b l e ) . T hr e e i d e n t i c a l f l a s hbu l b s A , B a n d C a r e s c r e w e d i n t o t h e i r s o c k e t s a n d a r e l i gh t e d wh e n t h e c i r c u i t i s c l o s e d . Af t e r e ac h o f t h e c h a ng e s s ugg e s t e d i n t h e fo l l ow i n g l e t t e r e d qu e s ti on s ( a -g) , t h e s y s t e m i s r e t ur n e d t o t h e i n i ti a l c ond i ti o n s how n i n t h e f i gur e b e for e t h e n e x t c h a ng e i s m a d e . T h e qu e s t i o n “ W h a t h a pp e n s t o …” r e f e r s t o wh e t h e r t h e qu a n t i t y i n qu e s ti o n i n c r e a s e s, d e c r e a s e s , o r r e m a i n s un c h a ng e d . I nd i c at e yo u r r e a s o n i n g b r i e f l y i n a n s w e r i n g e a c h q u e s t i o n . ( a ) Ho w d o t h e b r i gh t n e s s e s o f bu l b s A , B a n d C c o m p a r e w it h e a c h o t h e r i n t h e i n i t i a l c ond i ti o n ? (b ) B u l b A i s un s c r e w e d a n d r e m o v e d fro m i t s s o c k e t . ( N o t e : R e m o v i n g a bu l b f r o m i t s s o c k e t m e an s t ha t t h e c onn e c t i o n i s s e v e r e d a t t ha t po i n t , no t t h a t t h e b u l b i s r e p l a c e d b y a w i r e . ) i . W h a t h a p p e n s t o t h e br i g h t n e ss o f e a c h bu l b ? i i . W h a t s i m u l t a n e ou s l y h a pp e n s t o t h e c ur r e n t a t po i n t s 3 , 4 , a n d 5 ? ( c ) B u l b C i s un s c r e w e d a n d r e m o v e d fro m i t s s o c k e t i . W h a t h a pp e n s t o t h e br i gh t n e ss o f e a c h b u l b ? i i . W h a t s i m u l t a n e ou s l y h a pp e n s t o t h e c urr e n t a t p o i n t s 3 , 4 , a n d 5 ? (d ) A w i r e i s c onn e c t e d fro m t h e b a t t e r y t e r m i n a l a t po i n t 1 t o po i n t 4 . i . W h a t h a p p e n s t o t h e br i g h t n e ss o f e a c h bu l b ? i i . W h a t s i m u l t a n e ou s l y h a pp e n s t o t h e c urr e n t a t p o i n t 3 ? i i i . W h a t s i m u l t a n e ou s l y h a pp e n s t o t h e po t e n t i a l d i ff e r e n c e ac ro s s bu l b B ? i v . W h a t s i m u l t a n e ou s l y h a pp e n s t o t h e po t e n t i a l d i f f e r e n c e ac ro s s bu l b C ? v . W h a t s i m u l t a n e ou s l y h a p p e n s t o t h e po t e n t i a l d i ff e r e n c e b e t w e e n po i n t s 1 a n d 5 ? ( e ) A w i r e i s c onn e c t e d fro m t h e b a t t e r y t e r m i n a l a t po i n t 2 t o t h e s o c k e t t e r m i n a l a t po i n t 5 . i . W h a t h a p p e n s t o t h e br i g h t n e ss o f e a c h bu l b ? i i . W h a t h a p p e n s t o t h e c urr e n t a t po i n t 2 ? (f ) A fo u r t h b u l b ( D ) i s c onn e c t e d i n p a r a l l e l w i t h bu l b B a l on e , i . e . n o t i n p a r a l l e l w it h bo t h B a n d C . i . W h a t s i m u l t a n e ou s l y h a pp e n s t o t h e c urr e n t a t po i n t 3 ? i i . W h a t s i m u l t a n e ou s l y h a pp e n s t o t h e p o t e n t i a l d i ff e r e n c e b e t w e e n po i n t s 3 a n d 4 ? i i i . W h a t s i m u l t a n e ou s l y h a pp e n s t o t h e po t e n t i a l d i ff e r e n c e b e t w ee n po i n t s 2 a n d 4 ? (g ) T h e c onn e c t i o n i s brok e n a t po i n t 4 , a n d a r e s i s t o r i s i n t r odu ce d i n s e r i e s w i t h b u l b s B a n d C . W h a t w i l l h a pp e n t o t h e br i gh t n e ss o f e a c h bu l b ?

 

 

In the circuit shown above, the battery maintains a constant potential between points 1 and 2 (that is, the internal resistance of the battery is negligible).

 

Three identical flashbulbs A, B and C are screwed into their sockets and are lighted when the circuit is closed.  After each of the changes suggested in the following lettered questions (a-g), the system is returned to the initial condition shown in the figure before the next change is made.

 

The question “What happens to…” refers to whether the quantity in question increases, decreases, or remains unchanged.

Indicate your reasoning briefly in answering each question.

 

(a) How do the brightnesses of bulbs A, B and C compare with each other in the initial condition?

  

(b) Bulb A is unscrewed and removed from its socket. (Note: Removing a bulb from its socket means that the connection is severed at that point, not that the bulb is replaced by a wire.)

i. What happens to the brightness of each bulb?

 

ii. What simultaneously happens to the current at points 3, 4, and 5?

 

(c) Bulb C is unscrewed and removed from its socket i.  What happens to the brightness of each bulb?

 

ii. What simultaneously happens to the current at points 3, 4, and 5?

(d) A wire is connected from the battery terminal at point 1 to point 4. i. What happens to the brightness of each bulb?

 ii. What simultaneously happens to the current at point 3?

 

iii. What simultaneously happens to the potential difference across bulb B?

 

iv. What simultaneously happens to the potential difference across bulb C?

v. What simultaneously happens to the potential difference between points 1 and 5?

(e) A wire is connected from the battery terminal at point 2 to the socket terminal at point 5. i. What happens to the brightness of each bulb?

 

ii.  What happens to the current at point 2?

 

 

(f) A fourth bulb (D) is connected in parallel with bulb B alone, i.e. not in parallel with both B and C. i.  What simultaneously happens to the current at point 3?

 

ii. What simultaneously happens to the potential difference between points 3 and 4?

  

iii. What simultaneously happens to the potential difference between points 2 and 4?

 

  

(g)  The connection is broken at point 4, and a resistor is introduced in series with bulbs B and C.  What will happen to the brightness of each bulb?